This invention relates to a graphic processing method. More particularly, the invention relates to a graphic processing method in a system where a host computer is provided with an input of graphic data obtained by the execution of predetermined graphic processing, or in a system in which graphic data is received from a host computer, predetermined graphic processing is executed using the graphic data, and the obtained graphic is drawn.
Tablets and digitizers are widely known as graphic input devices for the entry of graphics into a computer. A graphic input device has the ability to sense coordinate values, specifically by sensing a position on a surface designated by, e.g., a stylus pen or cursor and entering the position into a host computer (host device) in the form of planar coordinate data (coordinates values in the XY plane, by way of example). Thus, a graphic input device senses, as point data, the coordinates of each point designated by a pen and sends a group of these items of point data to a host computer.
Thus, the data fed into the host computer in this fashion is point data and not graphic data indicative of straight lines and arcs. Even though the input data is point data, the data handled by the host computer is dealt with internally thereof not only as point data but also as straight lines (line segments), circles (circular arcs) or curves obtained by connecting these points, segments or arcs. The ultimate purpose of the host computer, moreover, is not to generate these straight lines, circles and curve data (graphic data) but to prepare an NC tape, create a three-dimensional curved surface or design mechanical parts on the basis of the generated graphic data, and to execute processing for attaining the particular purpose.
In the conventional arrangements, a host computer must be made to bear an extremely heavy load in order to take the step of entering point data into the host computer, generating graphic data from the point data and then executing processing for the final objective on the basis of these items of graphic data.
Accordingly, a method has been proposed wherein a graphic input device is provided with an intelligence function so that graphic data may be generated from point data by the graphic input device and sent to the host computer. Specifically, the method involves constructing the control and processing units of the graphic input device from a microcomputer or the like and executing the processing for graphic data creation on the terminal side. With a graphic input device having the above-described intelligence function, however, it is possible to execute only specific processing that is based on the program stored in the read-only memory (ROM) incorporated within the device. In other words, the graphic input device cannot be made to perform processing other than that specified. For instance, though the input device may have the ability to generate graphic data (line segments, circular arcs, curve data) from point data, the device cannot recognize characters from point data and transmit the characters to the host computer, cannot recognize alpha-numerics written by a pen and transmit the alphanumerics to the host computer, cannot attach the sense of circular arcs and straight lines or other optional functions to the abovementioned graphic data, and cannot create various data in accordance with the processing objective of the host computer. If it is attempted to force these functions upon the graphic input device, then it will be necessary to either replace the present ROM with a ROM for storing the desired processing program, or provide a ROM of large capacity, store various processing programs in the ROM and execute processing upon selecting the ROM prescribed for the particular objective. The former expedient is undesirable, however, because replacing the ROM is a troublesome task and ROMs storing the various processing programs must be prepared beforehand. The latter expedient entails a ROM of large capacity and raises cost. Overall system costs become particularly high in cases where a number of the input devices are connected to the host computer.
What has been set forth above regarding graphic input systems also applies to graphic output systems. Plotters and drafters are well-known as graphic output devices for preparing drawings based on graphic data produced at the output of a host computer. These graphic output devices continuously receive, e.g., pen positional data from the host computer and cause the pen to move on the basis of the positional data to produce a graphic. For example, in the case of a plotter, a curve which is desired to be written is converted by the host computer into a series of points on a predetermined plane, each item of point data for the various points obtained by the conversion is delivered to the plotter, and the plotter pen is transported on the basis of the point data to draw the curve in the form of an assemblage of points, as shown in FIG. 1. The conventional arrangement is undesirable, however, since the host computer is subjected to an increased burden owing to the construction which requires that the host computer convert the curve into the series of dots on the predetermined plane and then deliver the point data to the plotter.
Accordingly, the most common practice recently is to provide the output device with an intelligence function. An output device having an intelligence function is adapted to receive line segment or circular arc data from the host computer and perform interpolations based on the line segments or circular arcs to generate and draw curves composed of these segments and arcs. The control and processing units are constituted by a microcomputer or the like, so that the output device has the contruction of a computer. Thus a graphic output device has a ROM in which a predetermined graphic processing program is stored in advance, and is adapted to draw by performing graphic processing in accordance with the graphic processing program. Even though the graphic output device is provided with the intelligence function, however, the host computer must still generate the line segment data or circular arc data on the predetermined plane, so that the desired effect of lightening the burden is insufficient, though the burden is not as heavy as in the case where the data indicative of a series of points is generated. With a graphic output device having the above-described intelligence function, however, it is possible to execute only processing that is in accordance with the program stored in the ROM. In other words, the graphic output device either cannot be made to perform graphic processing other than that specified, or increases the load on the host computer. For instance, though the output device may have the ability to receive two-dimensional line segment data or circular arc data as an input thereto and draw curves on a predetermined plane, it cannot receive three-dimensional data and draw three-dimensional graphics (perspective views), as shown in FIGS. 2A and 2B, based on the three-dimensional data, nor can it draw a curved projection, obtained by projecting a curve onto any predetermined plane. When it is attempted to force these functions upon the graphic output device, it is necessary to either replace the present ROM with a ROM for storing the desired processing program, or provide a ROM of large capacity, store various processing programs in the ROM and execute processing upon selecting the ROM prescribed for the particular objective. The former method is undesirable, however, because replacing the ROM is a troublesome task and ROMs storing the various graphic processing programs must be prepared beforehand. The latter method requires a ROM of large capacity and raises cost.
Accordingly, an object of the present invention is to provide an easily operable graphic processing method that is capable of lightening the load borne by the host computer, and that enables the functions of a graphic input device and graphic output device to be changed, in a simple manner without modifying hardware.